President Barack Obama has declared victory in the battle over his controversial Obamacare health insurance reforms, declaring the law "is here to stay" after seven million Americans enrolled for health coverage.

The higher than expected figure comes at the end of a rocky first six months of enrolment, which began with the disastrous launch of the health reform's flagship website.

The technical glitches were eventually fixed and recent days have seen a surge of last-minute sign-ups ahead of the March 31 deadline to get insurance or face a fine.

In a triumphant speech from the White House, Mr Obama said the millions of Americans signing up for health coverage were evidence "this law is doing what it's supposed to do".

"The Affordable Care Act hasn't completely fixed our long-broken health care system, but this law has made our health care system a lot better," he said.

In a provocative jab at the law's long-time Republican critics, Mr Obama asked aloud: "Why are they so mad about the idea of folks having health insurance?"

Republicans countered that some of the seven million who have signed up under the reforms did so because they were driven off of their previous health plans.

Mr Obama had promised "If you like your insurance plan, you will keep it", and was forced to apologise after the law triggered the cancellation of many previous plans.

"Despite the White House 'victory lap,' this law continues to harm the American people," said a spokesman for John Boehner, the Republican speaker of the House.

"That's why we must replace this fundamentally-flawed law with patient-centred solutions that will actually lower health care costs and help create jobs."

In his White House address, Mr Obama accused Republicans of sniping at the law without offering alternatives to a healthcare system where Americans would often go bankrupt paying for medical bills.

"I've said before I will always work with anyone who's willing to make this law work even better. But the debate over repealing this law is over. The Affordable Care Act is here to stay," he said.

He conceded there would be "additional challenges" as the vastly complex healthcare law continues to be implemented, including crashes of the website.

An ABC/Washington Post poll this week showed the country evenly divided on Obamacare, with 49 per cent supporting the law and 48 per cent opposed.

That represents an improvement since November, when only 40 per cent approved and 57 per cent were opposed.

The issue remains politically difficult for Mr Obama's Democratic party and several Democrat senators facing uphill re-election battles in conservative states have been muted in their defence of the law.